Semiconductor module and power converter using the same

ABSTRACT

A semiconductor module may include a plurality of semiconductor elements; and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements. The plurality of semiconductor elements may include at least one upper arm switching element electrically connected between the first power terminal and the second power terminal; and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal. A number of the at least one upper arm switching element may be different from a number of the at least one lower arm switching element.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2019-028754, filed on Feb. 20, 2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The technology disclosed herein relates to a semiconductor module and a power converter using the same.

BACKGROUND

Japanese Patent Application Publication No. 2015-112015 describes a semiconductor module and a power converter using the same. The semiconductor module includes a plurality of semiconductor elements, and a first power terminal, a second power terminal and a third power terminal that are electrically connected to the plurality of semiconductor elements. The plurality of semiconductor elements includes an upper arm switching element electrically connected between the first power terminal and the second power terminal, and a lower arm switching element electrically connected between the second power terminal and the third power terminal.

SUMMARY

Providing a plurality of upper arm switching elements and a plurality of lower arm switching elements in the above-mentioned power converter can increase an allowable current which can be handled by the power converter. In this case, as one example, considerations are given to adding new upper and lower arm switching elements to inside of the semiconductor module. However, adding at least two switching elements inside the semiconductor module results in a significant increase in the size of the semiconductor module. Consequently, drastic design changes might be required not only for the semiconductor module but also for the power converter. On the other hand, considerations are also given to preparing a plurality of semiconductor modules and connecting them in parallel without changing the configuration of the semiconductor modules. In this case, design changes required for the power converter are often relatively less drastic. However, the increase in the number of semiconductor modules simply results in an increase in the size of the power converter. In view of this, the disclosure herein provides a technology that can at least partially solve such problems.

The technology disclosed herein allows the number of upper arm switching elements and the number of lower arm switching elements to be different from each other in one semiconductor module. Thus, the number of required semiconductor modules can be reduced, and further an increase in the size of each semiconductor module can be suppressed. For example, assuming that a power converter needs three upper arm switching elements and three lower arm switching elements. In this case, according to the present technology, two semiconductor modules are connected in parallel, only one new upper arm switching element is added to one of the two semiconductor modules, and only one new lower arm switching element is added to the other of the two semiconductor modules. Due to this, an increase in the number of required semiconductor modules can be suppressed, and further an increase in the size of each semiconductor module can be suppressed.

According to an aspect of the present technology, a semiconductor module is disclosed. The semiconductor module may include a plurality of semiconductor elements; and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements. The plurality of semiconductor elements may include at least one upper arm switching element electrically connected between the first power terminal and the second power terminal, and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal. A number of the at least one upper arm switching element may be different from a number of the at least one lower arm switching element.

In the semiconductor module described above, the at least one upper arm switching element may include a first switching element, and the at least one lower arm switching element may include a second switching element that has a same configuration as the first switching element. The at least one upper arm switching element or the at least one lower arm switching element may further include a third switching element having a different configuration from the first switching element. As another embodiment, the third switching element may have the same configuration as the first switching element and the second switching element. Herein, two switching elements having the same configuration means that the two switching elements are configured to have the same configuration (in terms of size, material, structure, etc.), except for inevitable differences therebetween due to the manufacture.

In one embodiment of the present technology, the first switching element may be mainly constituted of a first type of semiconductor material, and the third switching element may be mainly constituted of a second type of semiconductor material different from the first type of semiconductor material. Constituting the first switching element and the third switching element of different semiconductor materials allows their characteristics to significantly differ. Due to this, these two switching elements with the different characteristics can be selectively used, for example, depending on an index related to the semiconductor module (for example, a current value).

In the embodiment described above, a band gap of the second type of semiconductor material may be wider than a band gap of the first type of semiconductor material. In this case, for example, the first type of semiconductor material may be silicon (Si), and the second type of semiconductor material may be silicon carbide (SiC), a nitride semiconductor such as gallium nitride (GaN), or an oxide semiconductor. However, a specific combination of the first type of semiconductor material and the second type of semiconductor material is arbitrary and is not limited to these examples.

Additionally or alternatively to the above, a size of the third switching element may be smaller than a size of the first switching element. If the size of the third switching element is relatively small, adding the third switching element to an existing semiconductor module can suppress an increase in the size of the semiconductor module, for example.

According to another aspect of the present technology, a power converter is further disclosed herein. The power converter may include a first semiconductor module and a second semiconductor module electrically connected to the first semiconductor module. Each of the first semiconductor module and the second semiconductor module may include a plurality of semiconductor elements; and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements. The plurality of semiconductor elements may include at least one upper arm switching element electrically connected between the first power terminal and the second power terminal and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal. The first power terminal, the second power terminal and the third power terminal of the first semiconductor module may be electrically connected to the first power terminal, the second power terminal and the third power terminal of the second semiconductor module, respectively. In the first semiconductor module, a number of the at least one upper arm switching element may be greater than the number of the at least one lower arm switching element. In the second semiconductor module, a number of the at least one upper arm switching element may be smaller than a number of the at least one lower arm switching element.

In an embodiment of the present technology, a total number of the at least one upper arm switching element and the at least one lower arm switching element of the first semiconductor module may be equal to a total number of the at least one upper arm switching element and the at least one lower arm switching element of the second semiconductor module. With such a configuration, the first semiconductor module and the second semiconductor module can have the same or substantially the same size.

In an embodiment of the present technology, the power converter may further include a third semiconductor module. In this case, the third semiconductor module may include a plurality of semiconductor elements and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements. The plurality of semiconductor elements may include at least one upper arm switching element electrically connected between the first power terminal and the second power terminal, and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal. The first power terminal, the second power terminal and the third power terminal of the third semiconductor module may be electrically connected to the first power terminal, the second power terminal and the third power terminal of the second semiconductor module, respectively. In the third semiconductor module, a number of the at least one upper arm switching element may be equal to a number of the at least one lower arm switching element. By further combining the third semiconductor module with the first and second semiconductor modules, the number of the upper arm switching elements and the number of the lower arm switching elements can be adjusted appropriately.

In an embodiment of the present technology, the at least one upper arm switching element of the first semiconductor module and the at least one upper arm switching element of the second semiconductor module each may include a first switching element. The at least one lower arm switching element of the first semiconductor module and the at least one lower arm switching element of the second semiconductor module each may include a second switching element having a same configuration as the first switching element. The at least one upper arm switching element of the first semiconductor module and the at least one lower arm switching element of the second semiconductor module each may further include a third switching element having a different configuration from the first switching element. With such a configuration, the power converter can selectively use at least two types of switching elements depending on, for example, magnitude of electric power it needs to handle. Herein, two switching elements having the same configuration means that the two switching elements are configured to have the same configuration (in terms of size, material, structure, etc.) except for inevitable differences therebetween due to the manufacture.

In the embodiment described above, the power converter may further include a controller configured to control operations of the first semiconductor module and the second semiconductor module. In this case, the controller may be configured to perform a first switching control under which the third switching elements of the first semiconductor module and the second semiconductor module are driven in a complementary manner and the first switching elements and the second switching elements of the first semiconductor module and the second semiconductor module are not driven. Under the first switching control, the two switching elements located in the different semiconductor modules are driven, by which an increase in the temperature of each semiconductor module can be suppressed.

In the embodiment described above, the controller may be further configured to perform a second switching control under which at least one of the first switching elements of the first semiconductor module and the second semiconductor module and at least one of the second switching elements of the first semiconductor module and the second semiconductor module are driven in a complementary manner and the third switching elements of the first semiconductor module and the second semiconductor module are not driven. With such a configuration, power conversion efficiency can be enhanced by selectively performing the first switching control and the second switching control depending on, for example, the magnitude of electric power the power converter needs to handle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit block diagram showing a configuration of a power converter 10 of an embodiment.

FIG. 2 is a circuit block diagram showing a configuration of a U-phase switching circuit 12. A V-phase switching circuit 14 and a W-phase switching circuit 16 each also have the same configuration as the U-phase switching circuit 12.

FIG. 3 is a timing chart for explaining a first switching control and a second switching control.

FIG. 4 is a plan view showing an outer appearance of a first semiconductor module 20.

FIG. 5 is a cross-sectional view taken along a line V-V in FIG. 4 and schematically shows an internal structure of the first semiconductor module 20.

FIG. 6 is a plan view showing the internal structure of the first semiconductor module 20. In detail, FIG. 6 is a plan view perpendicular to a first conductor plate 42, and omits illustration of an encapsulant 28 and a second insulated circuit substrate 50.

FIG. 7 is a diagram with a second conductor plate 52 and a fourth conductor plate 54 added to the plan view shown in FIG. 6.

FIG. 8 is a perspective view of the first semiconductor module 20. Illustration of the encapsulant 28 is omitted.

FIG. 9 is a perspective view of the first semiconductor module 20. Illustration of the encapsulant 28 is omitted and the second insulated circuit substrate 50 is upwardly detached.

FIG. 10A shows an arrangement of a plurality of signal electrodes 22 d of a first switching element 22. FIG. 10B shows an arrangement of a plurality of signal electrodes 26 d of a third switching element 26.

FIG. 11 is a plan view showing an outer appearance of a second semiconductor module 70.

FIG. 12 is a cross-sectional view taken along a line XII-XII in FIG. 11 and schematically shows an internal structure of the second semiconductor module 70.

FIG. 13 is a plan view showing the internal structure of the second semiconductor module 70. FIG. 13 is a plan view perpendicular to a first conductor plate 92, and omits illustration of an encapsulant 78 and a second insulated circuit substrate 100.

FIG. 14 is a diagram with a second conductor plate 102 and a fourth conductor plate 104 added to the plan view shown in FIG. 13.

FIG. 15 is a perspective view of the second semiconductor module 70. Illustration of the encapsulant 78 is omitted.

FIG. 16 is a perspective view of the second semiconductor module 70. Illustration of the encapsulant 78 is omitted and a second insulated circuit substrate 100 is upwardly detached.

FIG. 17 is a plan view showing an outer appearance of a third semiconductor module 120.

FIG. 18 is a cross-sectional view taken along a line XVIII-XVIII in FIG. 17 and schematically shows an internal structure of the third semiconductor module 120.

FIG. 19 is a perspective view of the third semiconductor module 120. Illustration of the encapsulant 78 is omitted and a second insulated circuit substrate 150 is upwardly detached.

FIG. 20 is a plan view showing an outer appearance of a first semiconductor module 20A of a variant.

FIG. 21 is a cross-sectional view taken along a line XXI-XXI in FIG. 20 and schematically shows an internal structure of the first semiconductor module 20A of the variant.

FIG. 22 is a plan view showing the internal structure of the first semiconductor module 20A of the variant. FIG. 22 is a plan view perpendicular to the first conductor plate 42, and omits illustration of the encapsulant 28 and the second insulated circuit substrate 50.

FIG. 23 is a diagram with the second conductor plate 52 and the fourth conductor plate 54 added to the plan view shown in FIG. 22.

FIG. 24 is a plan view showing an outer appearance of a first semiconductor module 20B of another variant.

FIG. 25 is a cross-sectional view taken along a line XXV-XXV in FIG. 24 and schematically shows an internal structure of the first semiconductor module 20B of the other variant.

FIG. 26 is a plan view showing the internal structure of the first semiconductor module 20B of the other variant. FIG. 26 is a plan view perpendicular to the first conductor plate 42, and omits illustration of the encapsulant 28 and the second insulated circuit substrate 50.

FIG. 27 is a diagram with the second conductor plate 52 and the fourth conductor plate 54 added to the plan view shown in FIG. 26.

FIG. 28 is a plan view showing an outer appearance of a second semiconductor module 70A of a variant.

FIG. 29 is a cross-sectional view taken along a line XXIX-XXIX in FIG. 28 and schematically shows an internal structure of the second semiconductor module 70A of the variant.

FIG. 30 is a plan view showing the internal structure of the second semiconductor module 70A of the variant. FIG. 30 is a plan view perpendicular to the first conductor plate 92, and omits illustration of the encapsulant 78 and the second insulated circuit substrate 100.

FIG. 31 is a diagram with the second conductor plate 102 and the fourth conductor plate 104 added to the plan view shown in FIG. 30.

DETAILED DESCRIPTION

In an embodiment of the present technology, the semiconductor module may further include a first conductor plate on which the at least one upper arm switching element is disposed; a second conductor plate opposed to the first conductor plate with the at least one upper arm switching element interposed therebetween; a third conductor plate on which the at least one lower arm switching element is disposed and which is arranged side by side with the first conductor plate in a first direction and is electrically connected to the second conductor plate; and a fourth conductor plate which is opposed to the third conductor plate with the at least one lower arm switching element interposed therebetween and is arranged side by side with the second conductor plate in the first direction. In this case, the first power terminal may be electrically connected to the first conductor plate, the second power terminal may be electrically connected to the second conductor plate or the third conductor plate, and the third power terminal may be electrically connected to the fourth conductor plate. With such a configuration, heat generated by each semiconductor element can be effectively dissipated from both sides thereof via a pair of the conductor plates.

In the embodiment described above, the first switching element and the second switching element may be arranged along the first direction. The third switching element may be located between the first switching element and the second switching element with respect to the first direction. The phrase “with respect to the first direction” herein means paying attention only to positional relationship in the first direction while ignoring positional relationship in a direction perpendicular to the first direction. The same applies to the same or similar phrases (for example, “with respect to the second direction”) throughout the disclosure herein.

In the embodiment described above, in a plan view perpendicular to the first conductor plate, a center of the third switching element may be offset from a straight line passing through respective centers of the first switching element and the second switching element. That is, the third switching element may be offset with respect to an arrangement of the first switching element and the second switching element.

In the embodiment described above, the third conductor plate may be electrically connected to the second conductor plate via a first coupling portion, and the third power terminal may be electrically connected to the fourth conductor plate via a second coupling portion. In this case, the first coupling portion and the second coupling portion may be located between the first switching element and the second switching element with respect to the first direction. This configuration is advantageous when a size of the third switching element is smaller than sizes of the first switching element and the second switching element, although not particularly limited so.

In the embodiment described above, the first coupling portion and the second coupling portion may be located on a same side relative to the third switching element with respect to a second direction parallel to the first conductor plate and perpendicular to the first direction. With such a configuration, a current pathway in the semiconductor module can be shortened because the first coupling portion and the second coupling portion are adjacent to each other.

In the embodiment described above, in a plan view perpendicular to the first conductor plate, the first coupling portion and the second coupling portion each may extend along the first direction and may be adjacent to each other in the second direction. With such a configuration, the first coupling portion and the second coupling portion extend along the third switching element, therefore a current pathway between the third switching element and the first coupling portion (or the second coupling portion) can be widened.

Alternatively, in the plan view perpendicular to the first conductor plate, the first coupling portion and the second coupling portion each may extend along the second direction and may be adjacent to each other in the first direction. With such a configuration, an interval between the first conductor plate and the third conductor plate and an interval between the second conductor plate and the fourth conductor plate can be increased, by which insulation between these conductor plates can be enhanced.

In another embodiment, the first coupling portion and the second coupling portion may be located opposite to each other relative to the third switching element with respect to the above-described second direction. With such a configuration, a current pathway between the third switching element and the third power terminal can be shortened by arranging the third switching element and the second coupling portion adjacent to each other.

In the embodiment described above, in the plan view perpendicular to the first conductor plate, the first coupling portion may extend along the second direction, and the second coupling portion may extend along the first direction. With such a configuration, particularly because the first coupling portion extends along the second direction, a space can be provided, for example, for connecting signal wiring to the third switching element.

In an embodiment of the present technology, in the plan view perpendicular to the first conductor plate, the first power terminal, the second power terminal, and the third power terminal may be arranged along the first direction. In this case, the third power terminal may be located between the first power terminal and the second power terminal. With such a configuration, each power terminal can be located close to its corresponding conductor plate.

In an embodiment of the present technology, if the third switching element is included in the at least one upper arm switching element, the first conductor plate may include a first protrusion protruding toward the third conductor plate along the first direction. Further, at least a part of the third switching element may be located at the first protrusion. By partly enlarging the first conductor plate in accordance with the size of the third switching element, the size of the semiconductor module can be reduced.

In the embodiment described above, the second conductor plate may include a second protrusion protruding toward the fourth conductor plate along the first direction and opposed to the first protrusion. In this case, at least a part of the second protrusion may be opposed to the first protrusion with the third switching element interposed therebetween. That is, a protrusion may be provided in the second conductor plate to correspond to the protrusion of the first conductor plate.

In the embodiment described above, the third conductor plate may include a third protrusion protruding toward the first conductor plate along the first direction and adjacent to the first protrusion in the second direction perpendicular to the first direction. In this case, the third conductor plate may be electrically connected to the second conductor plate at the third protrusion. With such a configuration, the size of the semiconductor module can be reduced.

In the embodiment described above, the fourth conductor plate may include a fourth protrusion protruding toward the second conductor plate along the first direction and at least partly opposed to the third protrusion. In this case, the fourth conductor plate may be electrically connected to the third power terminal at the fourth protrusion. With such a configuration, the size of the semiconductor module can be further reduced.

In an embodiment of the present technology, if the third switching element is included in the at least one lower arm switching element, the fourth conductor plate may include a fourth protrusion protruding toward the second conductor plate along the first direction. In this case, at least a part of the fourth protrusion may be opposed to the third conductor plate with the third switching element interposed therebetween. By partly enlarging the fourth conductor plate in accordance with the size of the third switching element, the size of the semiconductor module can be reduced.

In the embodiment described above, the second conductor plate may include a second protrusion protruding toward the fourth conductor plate along the first direction and adjacent to the fourth protrusion in the second direction perpendicular to the first direction. In this case, the second conductor plate may be electrically connected to the third conductor plate at the second protrusion. With such a configuration, the size of the semiconductor module can be further reduced.

In an embodiment of the present technology, the semiconductor module may further include a first insulated circuit substrate and a second insulated circuit substrate opposed to the first insulated circuit substrate with the plurality of semiconductor elements interposed therebetween. In this case, the first conductor plate and the third conductor plate may be provided in the first insulated circuit substrate, and the second conductor plate and the fourth conductor plate may be provided in the second insulated circuit substrate. The term “insulated circuit substrate” herein means an insulated substrate (for example, ceramic substrate) that has a conductor plate joined to one surface or both surfaces thereof, such as an Active Metal Brazed Copper (AMC) substrate, a Direct Bonded Coper (DBC) substrate, or a Direct Bonded Aluminum (DBA) substrate.

Representative, non-limiting examples of the present disclosure will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing aspects of the present teachings and is not intended to limit the scope of the present disclosure. Furthermore, each of the additional features and teachings disclosed below may be utilized separately or in conjunction with other features and teachings to provide improved semiconductor modules and/or power converters, as well as methods for using and manufacturing the same.

Moreover, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the present disclosure in the broadest sense, and are instead taught merely to particularly describe representative examples of the present disclosure. Furthermore, various features of the above-described and below-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.

Embodiments

Referring to the drawings, a power converter 10 of an embodiment will be described. The power converter 10 of the present embodiment is employed in an electrically powered vehicle, such as an electric vehicle, a hybrid vehicle, and a fuel cell vehicle, and is configured to convert electric power between a DC power source 2 and a motor 4. It should be noted that applications of the power converter 10 are not particularly limited. The power converter 10 can be widely employed in various apparatuses and facilities.

As shown in FIG. 1, the power converter 10 includes a U-phase switching circuit 12, a V-phase switching circuit 14, a W-phase switching circuit 16, and a controller 18 configured to control operations of the switching circuits 12, 14, and 16. The U-phase switching circuit 12 is electrically connected between the DC power source 2 and a U-phase terminal of the motor 4, and is configured to connect the U-phase terminal of the motor 4 selectively to one of a positive electrode and a negative electrode of the DC power source 2. The V-phase switching circuit 14 is electrically connected between the DC power source 2 and a V-phase terminal of the motor 4, and is configured to connect the V-phase terminal of the motor 4 selectively to one of the positive electrode and the negative electrode of the DC power source 2. The W-phase switching circuit 16 is electrically connected between the DC power source 2 and a W-phase terminal of the motor 4, and is configured to connect the W-phase terminal of the motor 4 selectively to one of the positive electrode and the negative electrode of the DC power source 2.

The U-phase switching circuit 12 includes a plurality of semiconductor modules 20, 70, and 120. The plurality of semiconductor modules 20, 70, and 120 are connected in parallel with each other. The number of semiconductor modules 20, 70, and 120 is not particularly limited. In the present embodiment, the plurality of semiconductor modules 20, 70, and 120 includes a first semiconductor module 20, a second semiconductor module 70, and a third semiconductor module 120. The V-phase switching circuit 14 and the W-phase switching circuit 16 each have the same configuration as the U-phase switching circuit 12, and each include the first semiconductor module 20, the second semiconductor module 70, and the third semiconductor module 120.

Each first semiconductor module 20 includes a plurality of semiconductor elements 22, 24 and 26 and a plurality of power terminals 32, 34 and 36 electrically connected to the plurality of semiconductor elements 22, 24 and 26. The plurality of power terminals 32, 34 and 36 includes a first power terminal 32, a second power terminal 34 and a third power terminal 36. The first power terminal 32 is connected to the positive electrode of the DC power source 2. The second power terminal 34 is connected to the motor 4. The third power terminal 36 is connected to the negative electrode of the DC power source 2.

The plurality of semiconductor elements 22, 24 and 26 includes at least one upper arm switching element 22, 26, and at least one lower arm switching element 24. The at least one upper arm switching element 22, 26 is electrically connected between the first power terminal 32 and the second power terminal 34, and the at least one lower arm switching element 24 is electrically connected between the second power terminal 34 and the third power terminal 36. The at least one upper arm switching element 22, 26 includes a first switching element 22 and a third switching element 26, and the at least one lower arm switching element 24 includes a second switching element 24, although this is merely an example. As above, each first semiconductor module 20 includes the two upper arm switching elements 22 and 26 and the one lower arm switching element 24. Thus, the number of the upper arm switching elements 22 and 26 is greater than the number of the lower arm switching element 24.

The first switching element 22 and the second switching element 24 have the same configuration as each other. On the other hand, the third switching element 26 has a different configuration from the first switching element 22 and the second switching element 24. In detail, the first switching element 22 and the second switching element 24 are mainly constituted of silicon (Si), while the third switching element 26 is mainly constituted of silicon carbide (SiC) having a wider band gap than silicon. Further, the size of the third switching element 26 is smaller than that of the first switching element 22 and the second switching element 24. In general, silicon carbide substrates have more excellent properties than silicon substrates, but are more expensive than silicon substrates. Therefore, by using silicon carbide as the material of the third switching element 26 which has a smaller size, characteristics of the first semiconductor module 20 can be improved, and further an increase in the manufacturing cost thereof can be suppressed.

The first switching element 22 and the second switching element 24 in the present embodiment are Reverse Conducting Insulated Gate Bipolar Transistors (RC-IGBTs) which are IGBTs including built-in freewheeling diodes, while the third switching element 26 is a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), although this is merely an example. It should be noted that the first switching element 22 and the second switching element 24 may be IGBTs that do not include a built-in freewheeling diode. In this case, another semiconductor element including a diode may be added. Alternatively, the first switching element 22 and the second switching element 24 may be MOSFETs. The third switching element 26 may be an RC-IGBT or an IGBT.

Each second semiconductor module 70 includes a plurality of semiconductor elements 72, 74 and 76 and a plurality of power terminals 82, 84 and 86 electrically connected to the plurality of semiconductor elements 72, 74 and 76. The plurality of power terminals 82, 84 and 86 includes a first power terminal 82, a second power terminal 84 and a third power terminal 86. Also in the second semiconductor module 70, the first power terminal 82 is connected to the positive electrode of the DC power source 2, the second power terminal 84 is connected to the motor 4, and the third power terminal 86 is connected to the negative electrode of the DC power source 2. That is, the first power terminal 82, the second power terminal 84 and the third power terminal 86 of the second semiconductor module 70 are electrically connected to the first power terminal 32, the second power terminal 34 and the third power terminal 36 of the corresponding first semiconductor module 20, respectively.

The plurality of semiconductor elements 72, 74 and 76 of the second semiconductor module 70 includes at least one upper arm switching element 72 and at least one lower arm switching element 74, 76. The at least one upper arm switching element 72 is electrically connected between the first power terminal 82 and the second power terminal 84, and the at least one lower arm switching element 74, 76 is electrically connected between the second power terminal 84 and the third power terminal 86. The at least one upper arm switching element 72 includes a first switching element 72, and the at least one lower arm switching element 74, 76 includes a second switching element 74 and a third switching element 76, although this is merely an example. As above, each second semiconductor module 70 includes the one upper arm switching element 72 and the two lower arm switching elements 74 and 76, thus the number of the lower arm switching elements 74 and 76 is greater than the number of the upper arm switching element 72.

Also in the second semiconductor module 70, the first switching element 72 and the second switching element 74 have the same configuration as each other, and the third switching element 76 has a different configuration from the first switching element 72 and the second switching element 74. Here, the first switching element 72 and the second switching element 74 in the second semiconductor module 70 have the same configuration as the first switching element 22 and the second switching element 24 of the first semiconductor module 20. Further, the third switching element 76 in the second semiconductor module 70 has the same configuration as the third switching element 26 in the first semiconductor module 20. That is, also in the second semiconductor module 70, the first switching element 72 and the second switching element 74 are mainly constituted of silicon (Si), while the third switching element 76 is mainly constituted of silicon carbide (SiC). Further, the size of the third switching element 76 is smaller than that of the first switching element 72 and the second switching element 74.

Here, in the first semiconductor module 20 and the second semiconductor module 70, the numbers of the switching elements 22, 24, 26, 72, 74 and 76 are not particularly limited. Although not particularly limited, in the power converter 10 of the present embodiment, a total number of the upper arm switching elements 22, 26 and the lower arm switching element 24 in the first semiconductor module 20 is equal to a total number of the upper arm switching element 72 and the lower arm switching elements 74, 76 in the second semiconductor module 70. Further, a total number of the upper arm switching elements 22, 26 and 72 in the first semiconductor module 20 and the second semiconductor module 70 is equal to a total number of the lower arm switching elements 24, 74 and 76 in the first semiconductor module 20 and the second semiconductor module 70.

Each third semiconductor module 120 includes a plurality of semiconductor elements 122 and 124 and a plurality of power terminals 132, 134 and 136 electrically connected to the plurality of semiconductor elements 122 and 124. The plurality of power terminals 132, 134 and 136 includes a first power terminal 132, a second power terminal 134 and a third power terminal 136. Also in the third semiconductor module 120, the first power terminal 132 is connected to the positive electrode of the DC power source 2, the second power terminal 134 is connected to the motor 4, and the third power terminal 136 is connected to the negative electrode of the DC power source 2. That is, the first power terminal 132, the second power terminal 134 and the third power terminal 136 of the third semiconductor module 120 are electrically connected to the first power terminal 32, the second power terminal 34 and the third power terminal 36 of the first semiconductor module 20, respectively.

The plurality of semiconductor elements 122 and 124 of the third semiconductor module 120 includes at least one upper arm switching element 122 and at least one lower arm switching element 124. The at least one upper arm switching element 122 is electrically connected between the first power terminal 132 and the second power terminal 134, and the at least one lower arm switching element 124 is electrically connected between the second power terminal 134 and the third power terminal 136. The at least one upper arm switching element 122 includes a first switching element 122, and the at least one lower arm switching element 124 includes a second switching element 124, although this is merely an example. The third semiconductor module 120 includes one upper arm switching element 122 and one lower arm switching element 124, thus the number of the upper arm switching element 122 is equal to the number of the lower arm switching element 124. The first switching element 122 and the second switching element 124 have the same configuration as each other, and this configuration is the same as the configuration of the first switching elements 22 and 72 and the second switching elements 24 and 74 in the other semiconductor modules 20 and 70.

As described above, the U-phase switching circuit 12 includes the three semiconductor modules 20, 70 and 120. The semiconductor modules 20, 70 and 120 include the at least one upper arm switching element 22, 26, 72 and 122, and the at least one lower arm switching element 24, 74, 76 and 124, respectively. In particular, the first semiconductor module 20 includes the two upper arm switching elements 22 and 26, and the number of the upper arm switching elements 22 and 26 is greater than the number of the lower arm switching element 24. Meanwhile, the second semiconductor module 70 includes the two lower arm switching elements 74 and 76, and the number of the lower arm switching elements 74 and 76 is greater than the number of the upper arm switching element 72. However, in the entire U-phase switching circuit 12, the total number of the upper arm switching elements 22, 26, 72 and 122 is equal to the total number of the lower arm switching elements 24, 74, 76 and 124.

The V-phase switching circuit 14 and the W-phase switching circuit 16 each have the same configuration as the U-phase switching circuit 12. That is, the V-phase switching circuit 14 and the W-phase switching circuit 16 each also include the plurality of semiconductor modules 20, 70, and 120, which includes the first semiconductor module 20, the second semiconductor module 70, and the third semiconductor module 120. Each of the switching circuits 12, 14, and 16 may include at least the first semiconductor module 20 and the second semiconductor module 70. Alternatively, each of the switching circuits 12, 14, and 16 may include three or more semiconductor modules. In either case, the total number of the upper arm switching elements 22, 26, 72 and 122 may be equal to the total number of the lower arm switching elements 24, 74, 76 and 124 in each of the switching circuits 12, 14 and 16, although not particularly limited so.

In the power converter 10 of the present embodiment, the number of the upper arm switching elements 22 and 26 is different from the number of the lower arm switching elements 24 in the first semiconductor modules 20, and the number of the upper arm switching elements 72 is different from the number of the lower arm switching elements 74 and 76 in the second semiconductor modules 70. Allowing for the difference between the number of the upper arm switching elements 22 and 26 and the number of the lower arm switching elements 24 in some semiconductor modules 20 as well as the difference between the number of the upper arm switching elements 72 and the number of the lower arm switching elements 74 and 76 in some semiconductor modules 70 as above can suppress an increase in the size of the respective semiconductor modules 20 and 70 and further can suppress the number of required semiconductor modules 20, 70 and 120. That is, in the power converter 10 of the present embodiment, only one third switching element 26 is added to each first semiconductor module 20, and only one third switching element 76 is added to each second semiconductor module 70, as compared to the third semiconductor modules 120. This can suppress an increase in the size of each first semiconductor module 20 as compared to a case where two third switching elements 26 and 76 are added to each first semiconductor module 20, and further can make the three semiconductor modules 20, 70 and 120 substantially the same size.

Next, referring to FIG. 3, the controller 18 will be described. The controller 18 is configured to control the operations of the U-phase switching circuit 12, the V-phase switching circuit 14, and the W-phase switching circuit 16 to convert the DC power from the DC power source 2 to three-phase AC power to be supplied to the motor 4. For the conversion, the controller 18 selectively performs a first switching control and a second switching control in accordance with a current command value CC. More specifically, the first switching control is performed in a period (A) during which the current command value CC is lower than a threshold value CX, and the second switching control is performed in a period (B) during which the current command value CC is higher than the threshold value CX.

Under the first switching control, the third switching elements 26 and 76 of the first semiconductor modules 20 and the second semiconductor modules 70 are driven in a complementary manner, and the other switching elements 22, 24, 72, 74, 122 and 124 are not driven. That is, only the switching elements 26 and 76 constituted of silicon carbide are driven. Since only the third switching elements 26 of the semiconductor modules 20 and only the third switching elements 76 of the semiconductor modules 70 are driven under the first switching control, an increase in the temperatures of the semiconductor modules 20 and 70 is suppressed.

Under the second switching control, the first switching elements 22, 72 and 122 of the first semiconductor modules 20, the second semiconductor modules 70, and the third semiconductor modules 120, and the second switching elements 24, 74 and 124 of the first semiconductor modules 20, the second semiconductor modules 70 and the third semiconductor modules 120 are driven in the complementary manner. That is, only the switching elements 22, 24, 72, 74, 122 and 124 constituted of silicon are driven. Thus, under the second switching control, a large number of switching elements 22, 24, 72, 74, 122 and 124 are driven in response to the relatively large current command value CC. Under the second switching control, the number of driven switching elements 22, 24, 72, 74, 122 and 124 may be changed depending on the current command value CC.

Next, referring to FIGS. 4 to 10, the configuration of each first semiconductor module 20 will be described. The first semiconductor module 20 includes the plurality of switching elements 22, 24 and 26 and an encapsulant 28 that encapsulates these switching elements 22, 24 and 26. As described above, the plurality of switching elements 22, 24 and 26 includes the first switching element 22, the second switching element 24, and the third switching element 26. Each of the switching elements 22, 24 and 26 is a power semiconductor element, such as a MOSFET or an IGBT. The encapsulant 28 is constituted of a resin such as an epoxy resin, although not particularly limited so. The encapsulant 28 of the present embodiment has substantially a plate shape and includes an upper surface 28 a and a lower surface 28 b located opposite to the upper surface 28 a. The encapsulant 28 further includes a first end surface 28 c that is adjacent to the upper surface 28 a and the lower surface 28 b and a second end surface 28 d that is adjacent to the upper surface 28 a and the lower surface 28 b and is located opposite to the first end surface 28 c. The shape of the encapsulant 28 is not limited to the shape exemplified in the present embodiment and can be changed as appropriate.

The first semiconductor module 20 further includes the plurality of power terminals 32, 34 and 36 and a plurality of signal terminals 38 a and 38 b. The plurality of power terminals 32, 34 and 36 and the plurality of signal terminals 38 a and 38 b are constituted of a conductor such as copper or other metal. The plurality of power terminals 32, 34 and 36 includes the first power terminal 32, the second power terminal 34 and the third power terminal 36. The power terminals 32, 34 and 36 extend from the outside of the encapsulant 28 to the inside thereof and are electrically connected to the plurality of switching elements 22, 24 and 26 inside the encapsulant 28. The power terminals 32, 34 and 36 protrude from the first end surface 28 c of the encapsulant 28 to the outside and extend in parallel with each other along the same plane.

The plurality of signal terminals 38 a and 38 b includes a plurality of first signal terminals 38 a and a plurality of second signal terminals 38 b. Each of the first signal terminals 38 a extends from the outside of the encapsulant 28 to the inside thereof and is electrically connected to the first switching element 22 or the third switching element 26, inside the encapsulant 28. Each of the second signal terminals 38 b extends from the outside of the encapsulant 28 to the inside thereof and is electrically connected to the second switching element 24, inside the encapsulant 28. Here, the signal terminals 38 a and 38 b may be connected to the switching elements 22, 24 and 26 via bonding wires or may be connected thereto directly without any bonding wire. The plurality of signal terminals 38 a and 38 b protrudes from the second end surface 28 d of the encapsulant 28 to the outside and extends in parallel with each other along the same plane. The plurality of signal terminals 38 a and 38 b is connected to a connector (not shown) of the controller 18.

The first switching element 22 includes a semiconductor substrate 22 a, an upper electrode 22 b, a lower electrode 22 c, and a plurality of signal electrodes 22 d. The semiconductor substrate 22 a of the first switching element 22 is a silicon substrate, although not particularly limited so. Each of the upper electrode 22 b, the lower electrode 22 c, and the plurality of signal electrodes 22 d is constituted of a conductor such as metal. The upper electrode 22 b and the plurality of signal electrodes 22 d are located on an upper surface of the semiconductor substrate 22 a, while the lower electrode 22 c is located on a lower surface of the semiconductor substrate 22 a. The first switching element 22 is a vertical semiconductor element that includes a pair of the electrodes 22 b and 22 c with the semiconductor substrate 22 a interposed therebetween. As described above, the first switching element 22 of the present embodiment is an RC-IGBT, and thus has an IGBT structure and a diode structure inside the semiconductor substrate 22 a. The upper electrode 22 b is connected to an emitter of the IGBT structure and an anode of the diode structure, while the lower electrode 22 c is connected to a collector of the IGBT structure and a cathode of the diode structure.

As shown in FIG. 10A, the plurality of signal electrodes 22 d of the first switching element 22 includes a Kelvin emitter pad KE, a sense emitter pad SE, a gate pad G, and a pair of temperature sense pads TA and TK. The Kelvin emitter pad KE outputs a signal that indicates a voltage of the emitter of the IGBT structure (or the upper electrodes 22 b). The sense emitter pad SE outputs a signal that indicates a current passing through the IGBT structure. The gate pad G is connected to a gate of the IGBT structure. The pair of temperature sense pads TA and TK outputs a signal that indicates a temperature of the first switching element 22. In the first switching element 22, only the sense emitter pad SE and the gate pad G among these signal electrodes 22 d are connected to their corresponding first signal terminals 38 a. The types and the number of the signal electrodes 22 d are not particularly limited, and various changes can be made thereto.

The second switching element 24 has the same configuration as the first switching element 22. That is, the second switching element 24 includes a semiconductor substrate 24 a, an upper electrode 24 b, a lower electrode 24 c, and a plurality of signal electrodes 24 d. It should be noted that the plurality of signal electrodes 24 d of the second switching element 24 is connected to the plurality of second signal terminals 38 b. The other configurations of the second switching element 24 can be understood with reference to the above description for the first switching element 22, and therefore a duplicate description is omitted.

The third switching element 26 includes a semiconductor substrate 26 a, an upper electrode 26 b, a lower electrode 26 c and a plurality of signal electrodes 26 d. The semiconductor substrate 26 a of the third switching element 26 is a silicon carbide substrate, and its size is smaller than the size of the semiconductor substrate 22 a of the first switching element 22, although not particularly limited so. Each of the upper electrode 26 b, the lower electrode 26 c, and the plurality of signal electrodes 26 d is constituted of a conductor such as metal. The upper electrode 26 b and the plurality of signal electrodes 26 d are located on an upper surface of the semiconductor substrate 26 a, while the lower electrode 26 c is located on a lower surface of the semiconductor substrate 26 a. Similar to the first switching element 22, the third switching element 26 is a vertical semiconductor element that includes a pair of electrodes 26 b and 26 c with the semiconductor substrate 26 a interposed therebetween. As described above, the third switching element 26 of the present embodiment is a MOSFET, and thus includes a MOSFET structure inside the semiconductor substrate 26 a. The upper electrode 26 b is connected to a source of the MOSFET structure, while the lower electrode 26 c is connected to a drain of the MOSFET structure.

As shown in FIG. 10B, the plurality of signal electrodes 26 d of the third switching element 26 includes a Kelvin source pad KS, a sense source pad SS, a gate pad G, and a pair of temperature sense pads TA and TK. The Kelvin source pad KS outputs a signal that indicates a voltage of the source of the MOSFET structure (or the upper electrode 24 b). The sense source pad SS outputs a signal that indicates a current passing through the MOSFET structure. The gate pad G is connected to a gate of the MOSFET structure. The pair of temperature sense pads TA and TK outputs a signal that indicates a temperature of the third switching element 26. In the third switching element 26, only the sense source pad SS, the Kelvin source pad KS, and the gate pad G among these signal electrodes 22 d are connected to their corresponding first signal terminals 38 a. The types and the number of the signal electrodes 26 d are not particularly limited, and various changes can be made thereto.

The first semiconductor module 20 further includes a first insulated circuit substrate 40 and a second insulated circuit substrate 50. The first insulated circuit substrate 40 includes an insulated substrate 48, inner conductor plates 42 and 44 provided on one surface of the insulated substrate 48, and an outer conductor plate 46 provided on another surface of the insulated substrate 48. The insulated substrate 48 is constituted of an insulator, for example, ceramic. Each of the inner conductor plates 42 and 44 and the outer conductor plate 46 is constituted of a conductor, for example, copper or other metal. The inner conductor plates 42 and 44 are located inside the encapsulant 28 and are electrically connected to one or more of the switching elements 22, 24 and 26. The outer conductor plate 46 is electrically insulated from the inner conductor plates 42 and 44 and is exposed at the lower surface 28 b of the encapsulant 28. The first insulated circuit substrate 40 also functions as a heat dissipating plate that dissipates heat of the switching elements 22, 24 and 26 to the outside of the encapsulant 28.

The second insulated circuit substrate 50 includes an insulated substrate 58, inner conductor plates 52 and 54 provided on one surface of the insulated substrate 58, and an outer conductor plate 56 provided on another surface of the insulated substrate 58. The insulated substrate 58 is constituted of an insulator, for example, ceramic. Each of the inner conductor plates 52 and 54 and the outer conductor plate 56 is constituted of a conductor, for example, copper or other metal. The inner conductor plates 52 and 54 are located inside the encapsulant 28 and are electrically connected to one or more of the switching elements 22, 24 and 26. The outer conductor plate 56 is electrically insulated from the inner conductor plates 52 and 54 and is exposed at the upper surface 28 a of the encapsulant 28. The second insulated circuit substrate 50 also functions as a heat dissipating plate that dissipates heat of the switching elements 22, 24 and 26 to the outside of the encapsulant 28.

Each of the insulated circuit substrates 40 and 50 is, for example, an Active Metal Brazed Copper (AMC) substrate, a Direct Bonded Copper (DBC) substrate, or a Direct Bonded Aluminum (DBA) substrate, although not particularly limited so. The same applies to other insulated circuit substrates described herein.

The inner conductor plates 42 and 44 of the first insulated circuit substrate 40 include a first conductor plate 42 and a third conductor plate 44. The first conductor plate 42 and the third conductor plate 44 are located side by side along a first direction (direction parallel to an X-axis in the drawings). The inner conductor plates 52 and 54 of the second insulated circuit substrate 50 include a second conductor plate 52 and a fourth conductor plate 54. The second conductor plate 52 and the fourth conductor plate 54 are also located side by side along the first direction (X) and are opposed to the first conductor plate 42 and the third conductor plate 44, respectively. The first power terminal 32 is electrically connected to the first conductor plate 42, and the second power terminal 34 is electrically connected to the third conductor plate 44. The second power terminal 34 may be electrically connected to the second conductor plate 52, instead of the third conductor plate 44. The third power terminal 36 is electrically connected to the fourth conductor plate 54.

The first switching element 22 and the third switching element 26, which are the upper arm switching elements, are disposed on the first conductor plate 42. The lower electrode 22 c of the first switching element 22 and the lower electrode 26 c of the third switching element 26 are joined to the first conductor plate 42, for example, by soldering. The second conductor plate 52 is opposed to the first conductor plate 42 with the first switching element 22 and the third switching element 26 interposed therebetween. The upper electrode 22 b of the first switching element 22 and the upper electrode 26 b of the third switching element 26 are joined to the second conductor plate 52, for example, by soldering.

A conductor spacer 23 may be provided between the second conductor plate 52 (or the first conductor plate 42) and the switching element 22, and a conductor spacer 27 may be provided between the second conductor plate 52 (or the first conductor plate 42) and the switching element 26, as needed. In this case, the conductor spacer 23 for the first switching element 22 and the conductor spacer 27 for the third switching element 26 may have different structures and/or be constituted of different materials. Since the first switching element 22 and the third switching element 26 are constituted of different semiconductor materials, they differ from each other in mechanical properties, such as Young's modulus and linear expansion coefficient. Therefore, the conductor spacers 23 and 27, which are joined to the respective switching elements 22 and 26, may be given different mechanical properties by differentiating their structures and/or materials.

The second switching element 24, which is the lower arm switching element, is disposed on the third conductor plate 44. The lower electrode 24 c of the second switching element 24 is joined to the third conductor plate 44, for example, by soldering. The fourth conductor plate 54 is opposed to the third conductor plate 44 with the second switching element 24 interposed therebetween. The upper electrode 24 b of the second switching element 24 is joined to the fourth conductor plate 54, for example, by soldering. A conductor spacer 25 may be provided between the fourth conductor plate 54 (or the third conductor plate 44) and the second switching element 24, as needed. In this case, the conductor spacer 25 for the second switching element 24 and the conductor spacer 27 for the third switching element 26 may have different structures and/or may be constituted of different materials.

Here, in the first insulated circuit substrate 40, the outer conductor plate 46 is divided into a plurality of conductor plates, corresponding to the plurality of divided inner conductor plates 42 and 44. Due to this, warpage of the first insulated circuit substrate 40 caused by its thermal deformation can be suppressed. Similarly, also in the second insulated circuit substrate 50, the outer conductor plate 56 is divided into a plurality of conductor plates, corresponding to the plurality of divided inner conductor plates 52 and 54. Due to this, warpage of the second insulated circuit substrate 50 caused by its thermal deformation can be suppressed.

The first semiconductor module 20 further includes a first coupling portion 60 and a second coupling portion 62. The first coupling portion 60 electrically connects between the second conductor plate 52 and the third conductor plate 44, inside the encapsulant 28. The first coupling portion 60 is constituted of a conductor such as copper or other metal. The first coupling portion 60 is located between the second conductor plate 52 and the third conductor plate 44 and is joined to each of the conductor plates 44 and 52, for example, by soldering. The first coupling portion 60 may be integrally formed with the second conductor plate 52 or the third conductor plate 44. Alternatively, the first coupling portion 60 may be constituted of a solder or other joint material only.

The second coupling portion 62 electrically connects between the fourth conductor plate 54 and the third power terminal 36, inside the encapsulant 28. The second coupling portion 62 is constituted of a conductor such as copper or other metal. The second coupling portion 62 is located between the fourth conductor plate 54 and the third power terminal 36 and is joined to the fourth conductor plate 54 and the third power terminal 36, for example, by soldering. The second coupling portion 62 may be integrally formed with the fourth conductor plate 54 and/or the third power terminal 36. Alternatively, the second coupling portion 62 may be constituted of a solder or other joint material only.

In the first semiconductor module 20 with the configuration described above, the first switching element 22 and the second switching element 24 are arranged along the first direction (X). Then, the third switching element 26 is located between the first switching element 22 and the second switching element 24 with respect to the first direction (X). According to this configuration, the switching element 26, which has the different configuration from the switching elements 22 and 24, is disposed between the two switching elements 22 and 24 having the same configuration, by which structural symmetry of the first semiconductor module 20 can be enhanced. In particular, the third switching element 26 constituted of silicon carbide has different mechanical properties, such as Young's modulus and linear expansion coefficient, from the first switching element 22 and the second switching element 24 constituted of silicon. Disposing such third switching element 26 between the first switching element 22 and the second switching element 24 homogenizes stress and heat distribution generated inside the first semiconductor module 20.

In the first semiconductor module 20 of the present embodiment, in a plan view perpendicular to the first conductor plate 42 (see FIG. 6), the center of the third switching element 26 is offset from a straight line L that passes through the respective centers of the first switching element 22 and the second switching element 24. That is, the third switching element 26 is offset with respect to the arrangement of the first switching element 22 and the second switching element 24. Then, the first coupling portion 60 and the second coupling portion 62 are also located between the first switching element 22 and the second switching element 24 with respect to the first direction (X). Such a configuration allows the size of the first semiconductor module 20 to be reduced, since the third switching element 26 is smaller in size than the first switching element 22 and the second switching element 24.

In the first semiconductor module 20 of the present embodiment, the first coupling portion 60 and the second coupling portion 62 are located on the same side relative to the third switching element 26 with respect to a second direction (Y) that is parallel to the first conductor plate 42 and perpendicular to the first direction (X). With such a configuration, the first coupling portion 60 and the second coupling portion 62 are adjacent to each other, so a current pathway in the first semiconductor module 20 can be shortened. Further, in the plan view perpendicular to the first conductor plate 42 (see FIG. 6), the first coupling portion 60 and the second coupling portion 62 each extend along the second direction (Y) and are adjacent to each other in the first direction (X). With such a configuration, an interval between the first conductor plate 42 and the third conductor plate 44 and an interval between the second conductor plate 52 and the fourth conductor plate 54 can be increased, and thus insulation between these conductor plates 42, 44, 52 and 54 can be enhanced.

In the first semiconductor module 20 of the present embodiment, the first conductor plate 42 includes a first protrusion 42 a protruding toward the third conductor plate 44 along the first direction (X). Then, the third switching element 26 is disposed on the first protrusion 42 a. By partly enlarging the first conductor plate 42 corresponding to the size of the third switching element 26, the size of the first semiconductor module 20 can be reduced. In the present embodiment, an entirety of the third switching element 26 is disposed on the first protrusion 42 a of the first conductor plate 42. However, as another embodiment, only a part of the third switching element 26 may be disposed on the first protrusion 42 a of the first conductor plate 42.

In addition, the second conductor plate 52 includes a second protrusion 52 a that protrudes toward the fourth conductor plate 54 along the first direction (X) and is opposed to the first protrusion 42 a. A part of or an entirety of the second protrusion 52 a is opposed to the first protrusion 42 a with the third switching element 26 interposed therebetween. As described, the second protrusion 52 a can be provided in the second conductor plate 52 to correspond to the first protrusion 42 a of the first conductor plate 42.

In the first semiconductor module 20 of the present embodiment, the third conductor plate 44 includes a third protrusion 44 a protruding toward the first conductor plate 42 along the first direction (X). The third protrusion 44 a is adjacent to the first protrusion 42 a in the second direction (Y) perpendicular to the first direction (X). Then, the third conductor plate 44 is electrically connected to the second conductor plate 52 at the third protrusion 44 a. That is, the first coupling portion 60 is located at the third protrusion 44 a of the third conductor plate 44. With such a configuration, the size of the first semiconductor module 20 can be reduced.

In addition, the fourth conductor plate 54 may include a fourth protrusion 54 a that protrudes toward the second conductor plate 52 along the first direction (X) and is at least partly opposed to the third protrusion 44 a. In this case, the fourth conductor plate 54 is electrically connected to the third power terminal 36 at the fourth protrusion 54 a. That is, the second coupling portion 62 is located at the fourth protrusion 54 a of the fourth conductor plate 54. With such a configuration, the size of the first semiconductor module 20 can be further reduced.

In the first semiconductor module 20 of the present embodiment, the first conductor plate 42 and the third conductor plate 44 are provided at the first insulated circuit substrate 40, and the second conductor plate 52 and the fourth conductor plate 54 are provided at the second insulated circuit substrate 50. However, the first conductor plate 42 and the third conductor plate 44 each may be constituted of an independent metal plate, for example, a copper plate, instead of the first insulated circuit substrate 40. Similarly, the second conductor plate 52 and the fourth conductor plate 54 each may be constituted of an independent metal plate, for example, a copper plate, instead of the second insulated circuit substrate 50. Specific configurations of the first conductor plate 42, the second conductor plate 52, the third conductor plate 44 and the fourth conductor plate 54 are not particularly limited, and various changes can be made thereto.

Next, referring to FIGS. 11 to 16, the configuration of each second semiconductor module 70 will be described. The second semiconductor module 70 includes the plurality of switching elements 72, 74 and 76 and an encapsulant 78 that encapsulates these switching elements 72, 74 and 76. As described above, the plurality of switching elements 72, 74 and 76 includes the first switching element 72, the second switching element 74, and the third switching element 76. Each of the switching elements 72, 74 and 76 is a power semiconductor element, such as a MOSFET or an IGBT. The encapsulant 78 is constituted of a resin, such as an epoxy resin, although not particularly limited so. The encapsulant 78 of the second semiconductor module 70 has the same shape as the encapsulant 28 of the first semiconductor module 20, and thus has an upper surface 78 a, a lower surface 78 b, a first end surface 78 c, and a second end surface 78 d. The shape of the encapsulant 78 is not limited to that exemplified in the present embodiment and can be changed as appropriate.

The second semiconductor module 70 further includes the plurality of power terminals 82, 84 and 86 and a plurality of signal terminals 88 a and 88 b. The plurality of power terminals 82, 84 and 86 includes the first power terminal 82, the second power terminal 84 and the third power terminal 86. The plurality of signal terminals 88 a and 88 b includes a plurality of first signal terminals 88 a and a plurality of second signal terminals 88 b. The plurality of power terminals 82, 84 and 86 protrudes from the first end surface 78 c of the encapsulant 78 to the outside thereof, while the plurality of signal terminals 38 a and 38 b protrudes from the second end surface 78 d of the encapsulant 78 to the outside. The plurality of power terminals 82, 84 and 86 and the plurality of signal terminals 88 a and 88 b in the second semiconductor module 70 have the same configurations and functions as the plurality of power terminals 32, 34 and 36 and the plurality of signal terminals 38 a and 38 b in the first semiconductor module 20, respectively. Therefore, the details of the plurality of power terminals 82, 84 and 86 and the plurality of signal terminals 88 a and 88 b in the second semiconductor module 70 can be understood by referring to the description for the first semiconductor module 20 described above, and thus a duplicate description is omitted.

Each of the first switching element 72 and the second switching element 74 in the second semiconductor module 70 has the same configuration as the first switching element 22 of the first semiconductor module 20. Thus, the first switching element 72 and the second switching element 74 include semiconductor substrates 72 a and 74 a, upper electrodes 72 b and 74 b, lower electrodes 72 c and 74 c, and a plurality of signal electrodes 72 d and 74 d, respectively. Similarly, the third switching element 76 of the second semiconductor module 70 has the same configuration as the third switching element 26 of the first semiconductor module 20, and thus includes a semiconductor substrate 76 a, an upper electrode 76 b, a lower electrode 76 c, and a plurality of signal electrodes 764. Therefore, the details of the switching elements 72, 74 and 76 in the second semiconductor module 70 can be understood by referring to the description for the first semiconductor module 20 described above, and thus a duplicate description is omitted.

The second semiconductor module 70 further includes a first insulated circuit substrate 90 and a second insulated circuit substrate 100. The first insulated circuit substrate 90 includes an insulated substrate 98, inner conductor plates 92 and 94 provided on one surface of the insulated substrate 98, and an outer conductor plate 96 provided on another surface of the insulated substrate 98. The insulated substrate 98 is constituted of an insulator, for example, ceramic. Each of the inner conductor plates 92 and 94 and the outer conductor plate 96 is constituted of a conductor, for example, copper or other metal. The inner conductor plates 92 and 94 are located inside the encapsulant 78 and are electrically connected to one or more of the switching elements 72, 74 and 76. The outer conductor plate 96 is electrically insulated from the inner conductor plates 92 and 94 and is exposed at the lower surface 78 b of the encapsulant 78. Also in the second semiconductor module 70, the first insulated circuit substrate 90 functions as a heat dissipating plate that dissipates heat of the switching elements 72, 74 and 76 to the outside of the encapsulant 78.

The second insulated circuit substrate 100 includes an insulated substrate 108, inner conductor plates 102 and 104 provided on one surface of the insulated substrate 108, and an outer conductor plate 106 provided on another surface of the insulated substrate 108. The insulated substrate 108 is constituted of an insulator, for example, ceramic. Each of the inner conductor plates 102 and 104 and the outer conductor plate 106 is constituted of a conductor, for example, copper or other metal. The inner conductor plates 102 and 104 are located inside the encapsulant 78 and are electrically connected to one or more of the switching elements 72, 74 and 76. The outer conductor plate 106 is electrically insulated from the inner conductor plates 102 and 104 and is exposed at the upper surface 28 a of the encapsulant 78. The second insulated circuit substrate 100 also functions as a heat dissipating plate that dissipates heat of the switching elements 72, 74 and 76 to the outside of the encapsulant 78.

The inner conductor plates 92 and 94 of the first insulated circuit substrate 90 include a first conductor plate 92 and a third conductor plate 94. The first conductor plate 92 and the third conductor plate 94 are located side by side along the first direction (the direction parallel to the X-axis in the drawings). The inner conductor plates 102 and 104 of the second insulated circuit substrate 100 include a second conductor plate 102 and a fourth conductor plate 104. The second conductor plate 102 and the fourth conductor plate 104 are located side by side along the first direction (X) and are opposed to the first conductor plate 92 and the third conductor plate 94, respectively. The first power terminal 82 is electrically connected to the first conductor plate 92, and the second power terminal 84 is electrically connected to the third conductor plate 94. The second power terminal 84 may be electrically connected to the second conductor plate 102, instead of the third conductor plate 94. The fourth conductor plate 54 is electrically connected to the third power terminal 36. These configurations are common with those of the first semiconductor module 20.

Only the first switching element 72 is disposed, as the upper arm switching element, on the first conductor plate 92 of the second semiconductor module 70. The lower electrode 72 c of the first switching element 72 is joined to the first conductor plate 92, for example, by soldering. The second conductor plate 102 is opposed to the first conductor plate 92 with the first switching element 72 interposed therebetween. The upper electrode 72 b of the first switching element 72 is joined to the second conductor plate 102, for example, by soldering. Also in the second semiconductor module 70, a conductor spacer 73 may be provided between the second conductor plate 102 (or the first conductor plate 92) and the first switching element 72, as needed.

The second switching element 74 and the third switching element 76 are disposed, as the lower arm switching elements, on the third conductor plate 94 of the second semiconductor module 70. The lower electrode 74 c of the second switching element 74 and the lower electrode 76 c of the third switching element 76 are joined to the third conductor plate 94, for example, by soldering. The fourth conductor plate 104 is opposed to the third conductor plate 94 with the second switching element 74 and the third switching element 76 interposed therebetween. The upper electrode 74 b of the second switching element 74 and the upper electrode 76 b of the third switching element 76 are joined to the fourth conductor plate 104, for example, by soldering. A conductor spacer 75 may be provided between the fourth conductor plate 104 (or the third conductor plate 94) and the switching element 74, and a conductor spacer 77 may be provided between the fourth conductor plate 104 (or the third conductor plate 94) and the switching element 76, as needed. In this case, the conductor spacer 77 for the third switching element 76 may have a different structure and/or may be constituted of a different material from the conductor spacers 73 and 75 for the first switching element 72 and the second switching element 74.

The second semiconductor module 70 further includes a first coupling portion 110 and a second coupling portion 112. The first coupling portion 110 electrically connects between the second conductor plate 102 and the third conductor plate 94, inside the encapsulant 78. The second coupling portion 112 electrically connects between the fourth conductor plate 104 and the third power terminal 86, inside the encapsulant 78. The first coupling portion 110 and the second coupling portion 112 in the second semiconductor module 70 have the same structures and functions as the first coupling portion 60 and the second coupling portion 62 in the first semiconductor module 20. The description for the first coupling portion 60 and the second coupling portion 62 in the above-described first semiconductor module 20 can be also applied to the first coupling portion 110 and the second coupling portion 112 in the second semiconductor module 70, unless otherwise mentioned. Thus, the duplicate description is omitted herein.

In the second semiconductor module 70 with the configuration described above, the first switching element 72 and the second switching element 74 are arranged along the first direction (X). Then, the third switching element 76 is located between the first switching element 72 and the second switching element 74 with respect to the first direction (X). This is the same as in the first semiconductor module 20, and thus stress and heat distribution generated inside the second semiconductor module 70 are also homogenized.

In the second semiconductor module 70, in a plan view perpendicular to the first conductor plate 92 (see FIG. 13), the center of the third switching element 76 is offset from a straight line L that passes through the respective centers of the first switching element 72 and the second switching element 74. That is, the third switching element 76 is offset with respect to the arrangement of the first switching element 72 and the second switching element 74. The first coupling portion 110 and the second coupling portion 112 are also located between the first switching element 72 and the second switching element 74 with respect to the first direction (X). With such a configuration, the size of the semiconductor module 70 can be reduced since the third switching element 76 is smaller in size than the first switching element 72 and the second switching element 74.

In the second semiconductor module 70, the first coupling portion 110 and the second coupling portion 112 are located on the same side relative to the third switching element 76 with respect to the second direction (Y). With such a configuration, the first coupling portion 110 and the second coupling portion 112 are adjacent to each other, so a current pathway in the second semiconductor module 70 can be shortened. Further, in the plan view perpendicular to the first conductor plate 92 (see FIG. 13), the first coupling portion 110 and the second coupling portion 112 each extend along the second direction (Y) and are adjacent to each other in the first direction (X). With such a configuration, an interval between the first conductor plate 92 and the third conductor plate 94 and an interval between the second conductor plate 102 and the fourth conductor plate 104 can be increased, and thus insulation between these conductor plates 92, 94, 102 and 104 can be enhanced.

In the second semiconductor module 70, the fourth conductor plate 104 includes a fourth protrusion 104 a protruding toward the second conductor plate 102 along the first direction (X). A part of or an entirety of the fourth protrusion 104 a is opposed to the third conductor plate 94 with the third switching element 76 interposed therebetween. By partly enlarging the fourth conductor plate 104 corresponding to the size of the third switching element 76, the size of the second semiconductor module 70 can be reduced. In addition, the second conductor plate 102 includes a second protrusion 102 a protruding toward the fourth conductor plate 104 along the first direction (X). The second protrusion 102 a is adjacent to the fourth protrusion 104 a in the second direction (Y) perpendicular to the first direction (X). Then, the second conductor plate 102 is electrically connected to the third conductor plate 94 at the second protrusion 102 a. That is, the first coupling portion 110 is located at the second protrusion 102 a of the second conductor plate 102. With such a configuration, the size of the second semiconductor module 70 can be reduced.

Next, referring to FIGS. 17 to 19, the configuration of each third semiconductor module 120 will be described. The configuration of the third semiconductor module 120 is equivalent to the configuration of the first semiconductor module 20 from which the third switching element 26 is removed. That is, the third semiconductor module 120 includes the first switching element 122, the second switching element 124, and an encapsulant 128 that encapsulates these switching elements 122 and 124. The encapsulant 128 has a substantially plate shape, as with the encapsulant 28 of the first semiconductor module 20, and includes an upper surface 128 a, a lower surface 128 b, a first end surface 128 c, and a second end surface 128 d.

The third semiconductor module 120 further includes the plurality of power terminals 132, 134 and 136 and a plurality of signal terminals 138 a and 138 b. The plurality of power terminals 132, 134 and 136 includes the first power terminal 132, the second power terminal 134 and the third power terminal 136. The plurality of signal terminals 138 a and 138 b includes a plurality of first signal terminals 138 a and a plurality of second signal terminals 138 b. The plurality of power terminals 132, 134 and 136 and the plurality of signal terminals 138 a and 138 b in the third semiconductor module 120 have the same configurations and functions as the plurality of power terminals 32, 34 and 36 and the plurality of signal terminals 38 a and 38 b in the first semiconductor module 20.

The third semiconductor module 120 further includes a first insulated circuit substrate 140 and a second insulated circuit substrate 150. The first insulated circuit substrate 140 and the second insulated circuit substrate 150 in the third semiconductor module 120 have the same structures and functions as the first insulated circuit substrate 40 and the second insulated circuit substrate 50 in the first semiconductor module 20, respectively. That is, the first insulated circuit substrate 140 includes an insulated substrate 148, inner conductor plates 142 and 144, and an outer conductor plate 146. The inner conductor plates 142 and 144 include a first conductor plate 142 and a third conductor plate 144. The second insulated circuit substrate 150 includes an insulated substrate 158, inner conductor plates 152 and 154, and an outer conductor plate 156. The inner conductor plates 152 and 154 include a second conductor plate 152 and a fourth conductor plate 154. The third conductor plate 144 is electrically connected to the second conductor plate 152 via a first coupling portion 160, and the fourth conductor plate 154 is electrically connected to the third power terminal 136 via a second coupling portion 162.

In the third semiconductor module 120, all signal electrodes 122 d of the first switching element 122 are connected to the plurality of first signal terminals 138 a, and this is different from the first semiconductor module 20. The other configurations of the third semiconductor module 120 are the same as those of the first semiconductor module 20, the duplicate description is omitted herein.

In the power converter 10 of the present embodiment, in each of the U-phase, V-phase, and W-phase switching circuits, the first semiconductor module 20, the second semiconductor module 70, and the third semiconductor module 120 may be stacked on each other in their thickness direction. In this case, the first semiconductor module 20 and the second semiconductor module 70 may be disposed adjacent to each other. Disposing the first semiconductor module 20 and the second semiconductor module 70 adjacent to each other results in reduction in a power loss caused by execution of the first switching control. That is, under the first switching control, the third switching elements 26 and 76 of the first semiconductor module 20 and the second semiconductor module 70 are driven in a complementary manner. At this time, inductances of the first and second semiconductor modules 20 and 70 disposed adjacent to each other can be reduced since magnetic fields generated by energization of the semiconductor modules cancel out each other.

A cooler that uses a refrigerant, such as cooling water, may be interposed between the semiconductor modules 20, 70 and 120. In this case, to suppress an increase in the temperatures of the first semiconductor module 20 and the second semiconductor module 70, the first semiconductor module 20 and the second semiconductor module 70 may be disposed upstream of the refrigerant in the cooler.

FIGS. 20 to 23 show a first semiconductor module 20A of a variant. The configurations of the first coupling portion 60 and the second coupling portion 62 in this first semiconductor module 20A are different, compared to those of the first semiconductor module described above. Specifically, in the first semiconductor module 20A of the present variant, in the plan view perpendicular to the first conductor plate 42 (see FIG. 22), the first coupling portion 60 and the second coupling portion 62 each extend along the first direction (X) and are adjacent to each other in the second direction (Y). With such a configuration, the first coupling portion 60 and the second coupling portion 62 extend along the third switching element 26, by which the current pathway between the third switching element 26 and the first coupling portion 60 (or the second coupling portion 62) can be widened. Due to the above difference, the shapes of the first conductor plate 42, the second conductor plate 52, the third conductor plate 44, and the fourth conductor plate 54 are also different.

The other configurations of the first semiconductor module 20A are the same as those of the first semiconductor module 20 shown in FIGS. 4 to 10. Due to this, in FIGS. 20 to 23, the same or corresponding configurations as those of the first semiconductor module 20 are given the same reference signs. The other configurations of the first semiconductor module 20A can be understood with reference to the description for the above-described first semiconductor module 20, and thus the duplicate description is omitted.

FIGS. 24 to 27 show a first semiconductor module 20B of another variant. The configurations of the first coupling portion 60 and the second coupling portion 62 in this semiconductor module 20B are different, compared to those of the first semiconductor module described above. In the first semiconductor module 20B of the present variant, the first coupling portion 60 and the second coupling portion 62 are located opposite to each other relative to the third switching element 26 with respect to the second direction (Y). That is, in the plan view perpendicular to the first conductor plate 42 (see FIG. 26), the first coupling portion 60 is located on a second end surface 28 d side of the encapsulant 28, and the second coupling portion 62 is located on a first end surface 28 c side of the encapsulant 28. Further, the first coupling portion 60 extends along the second direction (Y), and the second coupling portion 62 extends along the first direction (X).

In addition, a plurality of signal relay paths 49 is provided at the first insulated circuit substrate 40. Some of the first signal terminals 38 a are connected to the signal electrodes 26 d of the third switching element 26 via the plurality of signal relay paths 49. The plurality of signal relay paths 49 extends along the second direction (Y) in parallel with the first coupling portion 60, although this is merely an example. In other words, because the first coupling portion 60 extends along the second direction (Y), a space where the plurality of signal relay paths 49 is provided can be ensured in the insulated substrate 48 of the first insulated circuit substrate 40.

The other configurations of the first semiconductor module 208 are the same as those of the first semiconductor module 20 shown in FIGS. 4 to 10. Due to this, in FIGS. 24 to 27, the same or corresponding configuration as those of the first semiconductor module 20 are given the same reference signs. The other configurations of the first semiconductor module 20B can be understood by citing the description for the above-described first semiconductor module 20, and thus the duplicate description is omitted.

FIGS. 28 to 31 show a second semiconductor module 70A of a variant. The configurations of the first coupling portion 110 and the second coupling portion 112 in the second semiconductor module 70A are different, compared to those of the second semiconductor module 70 described above. In the second semiconductor module 70B of the present variant, in the plan view perpendicular to the first conductor plate 92 (see FIG. 30), the first coupling portion 110 and the second coupling portion 112 each extend along the first direction (X) and are adjacent to each other in the second direction (Y). With such a configuration, the first coupling portion 110 and the second coupling portion 112 extend along the third switching element 76, by which the current pathway between the third switching element 76 and the first coupling portion 110 (or the second coupling portion 112) can be widened. Due to the above-described difference, the shapes of the first conductor plate 92, the second conductor plate 102, the third conductor plate 94, and the fourth conductor plate 104 are also be different.

The other configurations of the second semiconductor module 70B are the same as those of the second semiconductor module 70 shown in FIGS. 11 to 16. Due to this, in FIGS. 28 to 31, the same or corresponding configurations as those of the second semiconductor module 70 are given the same reference signs. The other configurations of the second semiconductor module 70B can be understood by citing the description for the above-described second semiconductor module 70, and thus the duplicate description is omitted. 

What is claimed is:
 1. A semiconductor module, comprising: a plurality of semiconductor elements; and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements, wherein the plurality of semiconductor elements comprises: at least one upper arm switching element electrically connected between the first power terminal and the second power terminal; and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal, wherein a number of the at least one upper arm switching element is different from a number of the at least one lower arm switching element.
 2. The semiconductor module according to claim 1, wherein the at least one upper arm switching element comprises a first switching element, the at least one lower arm switching element comprises a second switching element having a same configuration as the first switching element, and the at least one upper arm switching element or the at least one lower arm switching element further comprises a third switching element having a different configuration from the first switching element.
 3. The semiconductor module according to claim 2, wherein the first switching element is mainly constituted of a first type of semiconductor material, and the third switching element is mainly constituted of a second type of semiconductor material different from the first type of semiconductor material.
 4. The semiconductor module according to claim 3, wherein a band gap of the second type of semiconductor material is wider than a band gap of the first type of semiconductor material.
 5. The semiconductor module according to claim 2, wherein a size of the third switching element is smaller than a size of the first switching element.
 6. The semiconductor module according to claim 2, further comprising: a first conductor plate on which the at least one upper arm switching element is disposed; a second conductor plate opposed to the first conductor plate with the at least one upper arm switching element interposed therebetween; a third conductor plate on which the at least one lower arm switching element is disposed, the third conductor plate being arranged side by side with the first conductor plate in a first direction and being electrically connected to the second conductor plate; and a fourth conductor plate opposed to the third conductor plate with the at least one lower arm switching element interposed therebetween and arranged side by side with the second conductor plate in the first direction, wherein the first power terminal is electrically connected to the first conductor plate, the second power terminal is electrically connected to the second conductor plate or the third conductor plate, and the third power terminal is electrically connected to the fourth conductor plate.
 7. The semiconductor module according to claim 6, wherein the first switching element and the second switching element are arranged along the first direction, and the third switching element is located between the first switching element and the second switching element with respect to the first direction.
 8. The semiconductor module according to claim 7, wherein in a plan view perpendicular to the first conductor plate, a center of the third switching element is offset from a straight line passing through centers of the first switching element and the second switching element.
 9. The semiconductor module according to claim 7, wherein the third conductor plate is electrically connected to the second conductor plate via a first coupling portion, the third power terminal is electrically connected to the fourth conductor plate via a second coupling portion, the first coupling portion and the second coupling portion are located between the first switching element and the second switching element with respect to the first direction.
 10. The semiconductor module according to claim 9, wherein the first coupling portion and the second coupling portion are located on a same side relative to the third switching element with respect to a second direction parallel to the first conductor plate and perpendicular to the first direction.
 11. The semiconductor module according to claim 10, wherein in a plan view perpendicular to the first conductor plate, the first coupling portion and the second coupling portion each extend along the first direction and are adjacent to each other in the second direction.
 12. The semiconductor module according to claim 10, wherein in a plan view perpendicular to the first conductor plate, the first coupling portion and the second coupling portion each extend along the second direction and are adjacent to each other in the first direction.
 13. The semiconductor module according to claim 9, wherein the first coupling portion and the second coupling portion are located opposite to each other relative to the third switching element with respect to a second direction parallel to the first conductor plate and perpendicular to the first direction.
 14. The semiconductor module according to claim 13, wherein in a plan view perpendicular to the first conductor plate, the first coupling portion extends along the second direction, and the second coupling portion extends along the first direction.
 15. The semiconductor module according to claim 6, wherein in a plan view perpendicular to the first conductor plate, the first power terminal, the second power terminal, and the third power terminal are arranged along the first direction, and the third power terminal is located between the first power terminal and the second power terminal.
 16. The semiconductor module according to claim 6, wherein the third switching element is included in the at least one upper arm switching element, the first conductor plate comprises a first protrusion protruding toward the third conductor plate along the first direction, and at least a part of the third switching element is located at the first protrusion.
 17. The semiconductor module according to claim 16, wherein the second conductor plate comprises a second protrusion protruding toward the fourth conductor plate along the first direction and opposed to the first protrusion, and at least a part of the second protrusion is opposed to the first protrusion with the third switching element interposed therebetween.
 18. The semiconductor module according to claim 16, wherein the third conductor plate comprises a third protrusion protruding toward the first conductor plate along the first direction and adjacent to the first protrusion in a second direction perpendicular to the first direction, and the third conductor plate is electrically connected to the second conductor plate at the third protrusion.
 19. The semiconductor module according to claim 18, wherein the fourth conductor plate comprises a fourth protrusion protruding toward the second conductor plate along the first direction and at least partly opposed to the third protrusion, and the fourth conductor plate is electrically connected to the third power terminal at the fourth protrusion.
 20. The semiconductor module according to claim 6, wherein the third switching element is included in the at least one lower arm switching element, the fourth conductor plate comprises a fourth protrusion protruding toward the second conductor plate along the first direction, and at least a part of the fourth protrusion is opposed to the third conductor plate with the third switching element interposed therebetween.
 21. The semiconductor module according to claim 20, wherein the second conductor plate comprises a second protrusion protruding toward the fourth conductor plate along the first direction and adjacent to the fourth protrusion in a second direction perpendicular to the first direction, and the second conductor plate is electrically connected to the third conductor plate at the second protrusion.
 22. The semiconductor module according to claim 6, further comprising: a first insulated circuit substrate; and a second insulated circuit substrate opposed to the first insulated circuit substrate with the plurality of semiconductor elements interposed therebetween, wherein the first conductor plate and the third conductor plate are provided in the first insulated circuit substrate, and the second conductor plate and the fourth conductor plate are provided in the second insulated circuit substrate.
 23. A power converter, comprising: a first semiconductor module; and a second semiconductor module electrically connected to the first semiconductor module, wherein each of the first semiconductor module and the second semiconductor module comprises: a plurality of semiconductor elements; and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements, wherein the plurality of semiconductor elements comprises: at least one upper arm switching element electrically connected between the first power terminal and the second power terminal; and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal, wherein the first power terminal, the second power terminal and the third power terminal of the first semiconductor module are electrically connected to the first power terminal the second power terminal and the third power terminal of the second semiconductor module, respectively, in the first semiconductor module, a number of the at least one upper arm switching element is greater than a number of the at least one lower arm switching element, and in the second semiconductor module, a number of the at least one upper arm switching element is smaller than a number of the at least one lower arm switching element.
 24. The power converter according to claim 23, wherein a total number of the at least one upper arm switching element and the at least one lower arm switching element of the first semiconductor module is equal to a total number of the at least one upper arm switching element and the at least one lower arm switching element of the second semiconductor module.
 25. The power converter according to claim 23, further comprising a third semiconductor module, wherein the third semiconductor module comprises: a plurality of semiconductor elements, and a first power terminal, a second power terminal and a third power terminal electrically connected to the plurality of semiconductor elements, wherein the plurality of semiconductor elements comprises: at least one upper arm switching element electrically connected between the first power terminal and the second power terminal; and at least one lower arm switching element electrically connected between the second power terminal and the third power terminal, wherein the first power terminal, the second power terminal and the third power terminal of the third semiconductor module are electrically connected to the first power terminal, the second power terminal and the third power terminal of the second semiconductor module, respectively, and in the third semiconductor module, a number of the at least one upper arm switching element is equal to a number of the at least one lower arm switching element.
 26. The power converter according to claim 23, wherein the at least one upper arm switching element of the first semiconductor module and the at least one upper arm switching element of the second semiconductor module each comprise a first switching element, the at least one lower arm switching element of the first semiconductor module and the at least one lower arm switching element of the second semiconductor module each comprise a second switching element having a same configuration as the first switching element, and the at least one upper arm switching element of the first semiconductor module and the at least one lower arm switching element of the second semiconductor module each further comprise a third switching element having a different configuration from the first switching element.
 27. The power converter according to claim 26, further comprising a controller configured to control operations of the first semiconductor module and the second semiconductor module, wherein the controller is configured to perform a first switching control under which the third switching elements of the first semiconductor module and the second semiconductor module are driven in a complementary manner and the first switching elements and the second switching elements of the first semiconductor module and the second semiconductor module are not driven.
 28. The power converter according to claim 27, wherein the controller is further configured to perform a second switching control under which at least one of the first switching elements of the first semiconductor module and the second semiconductor module and at least one of the second switching elements of the first semiconductor module and the second semiconductor module are driven in a complementary manner and the third switching elements of the first semiconductor module and the second semiconductor module are not driven. 